A universal characteristic of eukaryotic cells is their ability to move. The manifestations of this movement can be quite diverse, ranging from cytokinesis to muscle contraction. The molecular motor responsible for generating the force to produce this movement is the myosin molecule. Two pairs of heavy chains (-200kDa) and two pairs of light chains (16- 20kDa) make up the intact myosin molecule. The site of ATP cleavage, which generates this force, is in the globular head of the myosin heavy chain (MHC) while filament forming capability is located in the alpha helical tail. These features are shared by all conventional myosin molecules. Despite these similarities, myosins are encoded by numerous diverse sequences. For example, DNA probes encoding striated muscle MHC will not, under most circumstances, cross-hybridize with RNA from nonmuscle sources. The total MHC gene number in mammals has been estimated to be 10-15. The best studied MHC genes are those expressed in striated muscle. Members of this group of genes are clustered on two chromosomes and show developmental and tissue-specific regulation of expression. It is not clear why there are so many diverse MHC genes required to carry out cellular contractile processes. Despite intensive study and the availability of cloned genes and cDNAs encoding several MHCs, the precise sequences in the molecule responsible for its various functions have not yet been defined. The goals of this proposal are: 1. To determine how these genes are organized chromosomally and to relate their organization to their patterns of expression. 2. To determine the total number of different MHC genes that are expressed in humans and to examine the sequence basis for this diversity. 3. To identify the functional domains of the myosin molecule using bacterial and lower eukaryotic expression systems. These goals provide a means of combining molecular genetic analysis of MHC genes with an investigation of the proteins they encode. The myosin system provides an excellent opportunity to begin dissecting individual members of a complex multigene family.